Sensing antenna coupling



Aug. 31, 1948. T'. H. CLARK l SENSING ANTENNA COUPLING 2 sheets-'sheet 1 Filed NOV. 27, 1943 ATTORNEY Aug. 31, 1948. T. H. CLARK SENSINGrv ANTENNA COUPLING 2 Sheet s-Sheet 2 Filed NOV. 27, 1943 ATTORNEY Patented Aug. 31, 1948 SENSING ANTENNA .COUPLING Trevor H: Clark; New York;- Y.; assignor to:- Federal Telephone andRadio Corporation, New York',l N." Y.; a corporation -of Delaware Application.November 27, 1943, Serial No. 511,937.

This'inventionrelates to antenna systems and more particularly to systems forl couplingk vsensing antennas. used with. loop, directionV 'nders to transmission lines.

It is common. practice to. provide sensing antennas to.be used with loop direction ndersystems to; obtain ,the sense of'a. direction indication. Ina; proposed system, as shown in my Patent No; v234.19538,'[issued 'April29', A194g?, va direction iindinggantenna arrangement is disclosedfwherein thesensing` antenna and counterpoise are mounted at the apex oitvvo` direction iinder loops. This construction requires thatzseparate lines be used to transferenergy between each oi' thedirection finders loops and translating equipment. In such a structure, as in other structures in which the sensing antenna and its associated elements are connected over separate cable to a receiver or av transmitter, it is desirable that means be provided to secure proper impedance relationloetween the sensing antenna and. its associated transmission line. In general, this desired relation should be such that the impedance presented the sense antenna line is about the same as that presentedh bythe direction finder. loop an'- tenna to its associated line.- This-maybe accomplished by a' couplingcircuit comprising'a dummy loop arrangement for coupling the sense antennal to its transmission' line. The ordinary balanced transformer arrangement, while satisfactory insome respects, fails to fully solve the problem.

It is'anobject ofV my inventionto provide a coupling'circuit,y comprising a dummy loop, which will serve-ato couple'anv antenna-to a transmissionline; whilepresentinga desired impedance-tol thefline.

It yis' a further object-of my invention toprovide acoupling circuit comprising la dummy loop for couplinga sensingvantenna to itstransmission line; which Will-present to its line an' impedance substantially similar to thatk presented by the associated direction nderm loop antenna toits transmission'line. n

According to a featureof `my invention, Iprovideea'V coupling circuit comprising -a' dummy loop connected at-A one end to-afeeder transmission line; thefvdummyfloop having impedance characteristics substantially simulating the impedance characteristicsof an'associated loop'antenna', and serving to couple a sensing antenna and counterpoise to theirtransmission line. The simulating"v dummy-v loop preferably comprises shieldedV lines, with a. gap in-'theshield at the-end; to which thesensingfantennaris coupled;

` 1o claims: (ol. 250g-332,67*)

better understanding; of jmy-invention and theolrrjectsand"features thereof may be had-fr0m the particular description of *embodiments there'- oiimade` with reference to the accompanying drawing; inwhich:

Fig: 1 is afragmentary view, ,partially in section",` of a directionnder loop antenna and-sensing-antenna assembly, Withl acoupling` circuit comprising a dummy loop 4in accordance withmy. invention, fslrownin circuit dia-gram; Fig'. 1A` is'afmodication` of vae portionv of the circuit of Fig. 1`; and l Figs. 2 to 5'sh'oW- alternativeY circuit diagrams ocoupling circuit arrangementsin accordance with my invention. l

Turninggrst to Fig.' 1, I have disclosed partof av direction nder'loop'assembly, such as shown in my1copendinge-application, Serial No.A 478,081, aforesaid; In'this systemthere are provided two direction nderloops indicatedat lwand'l I. Direction nder loop IILfor example;` comprisesa central." conductor-v |2UL covered1 with a conductive liraidlwlich serves as a'shield for-the Adirection finden loop `and whichshieldI is provided lWith a gapor-openingat its apex.u At'direction' 'nder loopyli the conductor r'is indicatedv at I4. The' sensing-"antenna I5 iis mountedI on abracket` at thel=apex of -thislp and isassociated With'counter poise elements |62 Antenna-I5? and counterpoise' elements IB" are'- interconnected i by i means ofl'le'ads IIT; I8; respectively, andthe couplingcoil 2|;l

' (.'ondensers- -22 and 23l"are provided to'balance th`e= capacities of the antenna counterpoise-V assembly units and may `differin size considerably depending `on the ldegree vof unb'alance of the *capacities-lofthese parts; The antenna and counterpoise elements 15)? Ifare 4coupled toa dual transmission 'line- 2li-which is: similar to the transmission-linesusedfr feeding direction nder loop antennas" I0 and*I I I.

aref-not "essntial'to' an?K4 understanding of ffmyf invention'. Lfin'ef24= isprovided `with1an outer shield: ZIFand-two-conductors 25)' 26? These conductors 25- ZSSare-econnectedi'over resistance `elements 32;

sheath Zrllof senseeantenna feed-line 224i The dummy orV couplingloophaving-sides 292 30 is preferably made of* shieldedconductors,

i having-thesameimpedancecharacteristics:as the The direction finder`- loop' antenna feed-ing vlilies lare' not shown since they sist of a single wire loop so that its impedance is negligible with respect to the impedance to the coupling loop. This coupling loop assembly provides a structure similar to that-normally provided by the shielded directionnder loop-antennas I and I I and is constructed to have substantially the same impedance as such loops,

Resistance elements 32, 33 are provided to giveV the coupling loop wide band frequency characterf istics. A more complete description of the function of such resistance elements maybe hadr by reference to Patent No. 2,423,083, issued July 1, 1947 and assigned to the same assignee as the present application. If the direction nder loop antennas are not provided with these coupling resistances, then they should be omitted in the coupling loop. Since the impedance of the dummy or coupling loop is substantially the same as the impedance presented to their respective lines by the direction finder antenna loops, the desired impedance characteristics will be obtained for energy transfer from the antenna counterpoise elements. Impedance elements I9, 20 may be provided to substantially decouple the antenna counterpoise assembly from the coupling loop to reduce the impedance load introduced into the coupling loop, as viewed from line 24. Preferably, the midpoint between condensers 22 and 23 is connected to the shield 40 of coupling loop 2B to take care of any unbalanced currents that may occur therein.

In Fig. 1A is shown an alternative arrangement for the coupling means interconnected between antenna I and counterpoise I6. In this arrangement, two inductance coils I9A and 20A are substituted for the resistance elements I9 and 2,0, oi?` Fig. 1. In all other respects this circuit is the same as that shown in Fig. 1 and similar reference characters have been applied.

- Since the essential feature of my invention resides in providing a coupling arrangement which will substantially simulate in impedance characteristic the impedance characteristics of the shielded loop antennas, other alternative structures may be provided, for example, as illustrated in the separate Figures 2 to 5, inclusive. Since the illustrations of these various forms may be applied to the structural arrangement in an obvious manner, these modications'have been illustrated simply in circuit diagrams. lThe same reference characters alsol have been used throughout to designate similar elements.

In Fig. 2 is disclosed another form of my invention for inductively coupling antenna I5 and counterpoise I6 to transmission line 24. According to this arrangement, conductors 25 and 26 are coupled over resistance elements 32, 33 to hollow tubular members 45 and 46. Thus, an inductive coupling between the antenna and counterpoise arrangement I5, I6 and the transmission line 24 is provided by means of coil 4I. Preferably, the entire structure is housed within a shielded housing 4I] which is directly -connected to the outer sheath 2'I of feed line 24.

In Fig. 3 an arrangement substantially similar 4 to that in Fig. 2 is shown. However, in this arrangement a simple shielded loop 45A is provided in place of the two conductor pairs 45 and 46 of Fig. 2 and the remote end of this loop is not grounded.

In Fig. 4 is shown an arrangement substantially similar to that coupling arrangement shown in Fig. 1. However, in this arrangement resistive coupling of antenna I5 and counterpoise I6 is provided instead of the inductive coupling. To

this end conductors 29 and 3U are interconnected at their remote end by a coupling resistor 50. Re-

sistance elements I9 and 20 are also connected respectively to ends of coupling resistor 59. Each of resistors I9, are shunted by tuning condensers 5I, 5.2, as desired. The common coupling resistance 59 takes the place of the transformer sections 2|, 3| of Fig. 1 in providing the desired coupling between the antenna counterpoise I5, I6 and the lead line 24.

Fig. 5 is substantially identical with the structure of Fig.'4 except that condensers 5I, 52 are connected between the antenna ends of resistors I9, 20, respectively, and the respective shield members 35, and 36.

It will be clear to those skilled in the art that many other methods of constructing this apparatus. otherthan those specifically described vare readily constructed. It should be distinctly understood that the illustrations shown in the few modiiications of my invention rare made merely by way of illustration and are not to be considered as limitations on the scope of my invention, as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1In an antenna assembly, a loop antenna, a sensing antenna and counterpoise used in operative association with said loop antenna, a transmission line, a coupling circuit for coupling said sensing antenna and counterpoise to said transmission line to provide an impedance to said line substantially simulating the impedance of said loopv antenna comprising, a coupling loop having two legs connected at` one end to said,

, transmission linie, resistance means in each leg of said coupling loop adjacent said transmission line,.and a coupling .means connected to said sensing antenna and said counterpoise, and coupled to said coupling loop, to transfer energy between said Sensing antenna and said transmission line.

2. A coupling circuit according to claim 1 wherein said coupling loop comprises a coupling impedance connected between the legs of said coupling loop at its end remote from said transmission line, further comprising shield means aroundeach leg of said coupling loop and around said transmission line, and separate impedance means connected between the opposite legs of said coupling loop and said antenna and coun-` terpoise, respectively.

3. A coupling circuit according to claim 1, wherein said coupling loop comprises a relatively narrow coupling loop conguration and a. direct connection between the legs of said coupling loop remote from said transmission line, and said LA coupling circuit according to claim 1,

wherein saidcoupling means for said counterpoise comprises a single loop extending from lsaid antenna and counterpoise to a point adjacentl said coupling loop, and said coupling loop comprises shield conductors substantially surrounding said single loop.

5. In an antenna assembly, a shielded loop antenna, a sensing antenna and counterpoise used in association with said loop antenna, a dual conductor shielded transmission line, a coupling circuit coupling said sensing antenna and counterpoise to said transmission line to provide an impedance substantially simulating the impedance presented to its own transmission line by said loop antenna, a pair of loop conductors in said coupling circuit, each of said conductors connected at one end to separate of said conductors of said transmission line, individual shield means connected at one end to the shield of said transmission line and substantially surrounding said loop conductors, the remote ends of said individual shield means being spaced to provide a gap, whereby said coupling loop simulates the impedance of said loop antenna, an impedance element interconnecting the other ends of said loop conductors across said gap, and means for coupling said antenna and counterpoise with said impedance.

6. A coupling circuit according to claim 5, wherein said impedance element comprises an inductance means, and said last named means comprises a coil loosely coupled with said inductance means, and impedance means interconnecting opposite ends of said coil and said antenna and counterpoise.

7. A coupling circuit according to claim 5, wherein said last named means comprises 1mpedance means respectively in series With said antenna and said counterpoise, and condenser means coupled thereto.

8. A coupling circuit according to claim 5, wherein said impedance element comprises a resistance means, and said coupling means cornprises resistors connected in series between the ends of said resistance means and said antenna and counterpoise, respectively.

9. In an antenna assembly, a loop antenna, a sensing antenna and counterpoise used in operative association with said loop antenna, a transmission line, a coupling circuit for coupling said sensing antenna and counterpoiseto said transmission line to provide an impedance to said line substantially simulating the impedance of said loop antenna, a coupling loop in the coupling circuit of substantially the same length as said loop antenna and having substantially no effective height, said coupling loop being connected at one end to said transmission line, and a coupling means connected to said sensing antenna and said counterpoise, and coupled to said coupling loop, to transfer energy between said sensing antenna and said transmission line.

10. In an antenna assembly, a pair of shielded loop antennas, a sensing antenna and counterpoise used in operative association with said loop antennas, a dual conductor shielded transmission line, a coupling circuit coupling said sensing antenna and counterpoise to said transmission line to provide an impedance substantially simulating the impedance presented to its under transmission line by said loopantenna, said coupling circuit comprising a pair of loop conductors having substantially the same impedance characteristics as the conductors of said loop antennas and each loop conductor connected at one end to separate conductors of said transmission line, said loop conductors each having a length substantially equal to half the periphery of a loop antenna and arranged close to one another to provide substantially no eiective radiation height, individual shield means connected at o-ne end to the shield of said transmission line and surrounding said loop conductors, the remote ends of said individual shield means being spaced to provide a gap, whereby said loop conductors simulate the impedance of a loop antenna, an impedance element interconnecting the ends of said loop conductors across said gap, and means for coupling said sensing antenna and counterpoisewith said impedance.

TREVOR H. CLARK.

REFERENCES CITED The following references are of record in the lle of this patent:

UNITED STATES PATENTS Number Name Date 2,259,510 Alford Oct. 21, 1941 2,315,170 Van Weel Mar, 30, 1943 

